Answer:The purpose of including these details in his letter is to highlight the author's experience of being part of a minority group and the sense of solidarity he feels with other black individuals. By describing his encounter with "black" Italians and black Africans in Italy, the author is emphasizing the common bond that exists between people of African descent, regardless of their nationality or background.
The author's mention of how they used to acknowledge each other when growing up, passing boats in a sea of white people, further underscores the idea of shared experiences and the need for mutual recognition and understanding. This detail helps to illustrate the author's perspective and the importance of acknowledging and connecting with others who share similar racial or cultural backgrounds.
Overall, the inclusion of these details serves to convey the author's personal reflections on race, identity, and the significance of recognizing and acknowledging one another in a diverse world.